Combining Audio Inputs

[Zervife]

I have a digital piano (P-45) that has  1⁄4 inch output and I want to hear from both my P-45 and my laptop.
I have tried connecting the P-45 through USB to my laptop but when I use programs to hear from it, there's a significant delay, though no problems in recording MIDI and such.

Since I might want to connect many other inputs later on, I need a device that combines inputs

 

So I've googled and found that there are splitters (those that look like a Y or X or star whatever) for cheap, these aren't what I was looking for.
I then found a lot of these things:
https://www.presonus.com/products/audiobox-usb
https://www.amazon.com/Behringer-502-XENYX502-5-Channel-Mixer/dp/B000J5UEGQ
and many more.
I saw that most of these stuff has 4-pin XLR connectors, I really don't mind having them to use later on.

 

So I'm looking for suggestions as to which one of these things to get. (also what they're called) (Mixers?)

To add, my current laptop doesn't have an input jack (the one combined in/out 3.5mm jack broke), currently using a FiiO K1 USB DAC. If possible, I want one such 'box' that can be connected to my laptop through USB, icing on the cake would be S/PDIF output to connect to home theatre systems.

I'm quite flexible on the pricing but I'm not a professional and do not need super awesome professional gears.
I also haven't read about these much yet so please keep it simple. Thanks in advance for any help!